Process for the treatment of hydrocarbon oils



3,055,825 PROCESS FOR THE TREATMENT OF HYDROCARBON OILS Weigert C.Buningh and Cornelis D. Ten Have, Amsterdam, Netherlands, assignors toShell Oil Company, a corporation of Delaware No Drawing. Filed Dec. 29,1958, Ser. No. 783,166 Claims priority, application Netherlands Jan. 3,1958 21 Claims. (Cl. 208-254) This invention relates to a process forremoving nitrogen compounds from hydrocarbon oils. More particularly, itrelates to a process for removing nitrogen compounds from hydrocarbonoils containing olefins by means of solid adsorbents.

Almost all petroleum crude oils contain small amounts of variousnitrogenous compounds which are found in varying concentrations in thefractions and products produced from such crudes. Thesenitrogen-containing compounds have been identified as consisting of aryland alkyl amines, derivatives of pyridine, pyrroles, pyrazoles, andquinolines. When these compounds are present in hydrocarbon oilfractions such as lubricating oils, fuel oils, diesel oils, jet fuels,and gasolines, they may cause deposit or laquer formations in thesystems in which they are used. Moreover, such nitrogen compounds havebeen found to contribute to instability during storage and the formationof sludge, gum, and dark color. To avoid the adverse effects of whichnitrogenous compounds contribute, it is frequently desirable to removethem.

Many processes have been used and suggested for the removal of nitrogencompounds from hydrocarbon oils, among which are extraction withsulfuric acid, ion exchange, hydrotreating, and other means of removalby solid adsorbents. However, none of the means heretofore known havebeen entirely successful and the removal of nitrogen compounds frompetroleum hydrocarbons is not widely practiced in the United States. Theheretofore most promising of these processes has been hydrotreating ofthe hydrocarbon over a catalyst which is selective to Warddenitrification. However, in the case of gasolines containing olefins,this process has the severe disadvantage that a significant octanenumber loss is incurred by the partial hydrogenation of the high-octaneolefinic components. Sulfuric acid extraction has also been used withsome frequency. However, this process has been found to contribute togreater gum formation in the ex-.

because of the difficulty in desorbing the adsorbed ma-' terials andregenerating the expensive adsorbents effectively,.and further becauseof excessive regeneration time requirements.

.It' is. therefore an object of this invention to provide an improvedprocess for theremoval of nitrogen compounds from hydrocarbon oils. Itis a further object to provide a process for the removal of nitrogencompounds from hydrocarbon oils by means of an easily regenerated. It isa still further object of the invertsolid adsorbent. tion to provide anon-corrosive process for removal of nitrogen compounds from hydrocarbonoils. Another object is to provide a process for theremoval of nitrogencompounds from hydrocarbon oils in which olefinic con- Patented Sept.25, 1962 ire stituents of the oils are not adsorbed or polymerized. Yetanother object of the invention is to provide an adsorptive process forthe removal of nitrogen compounds from hydrocarbons in which theregeneration of the adsorbent is sufficiently rapid and complete as topermit the carrying out of the process in a continuous manner. Theforegoing objects will be apparent from the detailed description of theinvention.

The present invention is an improved process for the removal ofnitrogenous compounds from hydrocarbon oils which comprises passing thehydrocarbon which contains nitrogen compounds through a solid adsorbent,which has been pre-wetted with a polar organic liquid, until theadsorbent is saturated with nitrogenous compounds, and desorbing thenitrogen compounds, regenerating the adsorbent, and pre-wetting theadsorbent in a single operation by passing through it a mixture of polarorganic liquid and water.'

The process according to this invention may be applied to varioushydrocarbon oils containing nitrogenous compounds. However, it isparticularly advantageous for the removal of dissolved organic nitrogencompounds from hydrocarbon oils containing olefins, such as gasolinesand gas oils obtained by thermal or catalytic cracking or by thermalreforming. This process may also be applied to oil which has beenobtained from oil-bearing shale by exposing it to heating. The processis also useful for removing organic nitrogen compounds from distillationproducts obtained in the working up of tar, e.g., crude benzenefractions. The starting materials are preferably fractions which havealready been subjected to conventional pre-refining.

As the adsorbent for this invention, various high surface areaadsorption compounds may be used so long as they possess at leastmoderate base exchange capacity and a high surface area. change capacityof at least 15 mini-equivalents per grams and a surface area of at least100 M /gram are preferred. Examples of suitable adsorbents aresilicaprior to treatment of the nitrogenous hydrocarbons there with. Asa result of the pretreatment, the adsorbent retains its full capacity toadsorb organic nitrogen compounds. Moreover, the catalytic etfect of theadsorbent upon the polymerization of the unsaturated compoundsisprevented by the polar organic liquid adsorbed on the surface of theadsorption agent. It is preferred to use for the pretreatment of theadsorbent a polar organic liquid which has an adsorptive affinity forthe adsorbent approximately equal to that of the organic nitrogencompounds which are to be removed. Furthermore, it should be at leastpartially soluble in hydrocarbons. Fifty percent solubility of the polarorganic liquid in hydrocarbons is preferred and complete solubility isparticularly preferred. An adsorptive agent pretreated in the abovemanner can thus be regenerated and pretreated simultaneously by means ofthe polar organic liquid with which the adsorption agent must bepretreated.

The adsorbent may be pretreated with various polar organic liquids ormixtures thereof having approximately equal adsorption affinity for theadsorbent as the organic nitrogen compounds to be removed. Suitable forthis purpose are dialkyl ketones, esters of fatty acids, dialkyl ethers,cyclic ethers, alkanols, alkanediols, and monoethers thereof. Examplesof some of the specific compounds which may be used are acetone,butanone, ethyl Adsorbents having a base ex-' acetate, diethyl ether,diisopropyl ether, dioxane, methanol, ethanol, isopropyl alcohol,ethylene glycol, 2-ethoxyethanol, and diethylene glycol mono-methylether. In order that the adsortpive afiinity of the polar organic liquidapproximate that of the nitrogen compounds, it is preferred that itcontain not more than six carbon atoms per molecule. In the case ofdialkyl ketones, it is preferred that they contain less than six carbonatoms per molecule. Acetone is particularly preferred as the pretreatingfluid for practicing this invention.

Organic nitrogen compounds contained in hydrocarbon oils, e.g.,catalytically cracked gasoline, are effectively recovered by means ofthe foregoing adsorbents which have been pretreated by any of the abovepolar organic liquids or their mixtures until the adsorbent becomessaturated, which point may readily be detected by an increase in theamount of nitrogenous compounds in the treated hydrocarbon oil. Theadsorbent may be regenerated effectively and rapidly by first contactingit with a mixture comprising equal parts by volume of water and thepretreating polar organic liquid and subsequently with the polarpretreating liquid alone. These liquids may be passed down through theadsorbent to effect the regeneration. Any hydrocarbon oil still presentin the adsorbent is expelled by the mixture of water and pretreatingliquid. It is a unique and highly advantageous characteristic of thisinvention that during the regeneration step the water is elutriatedimmediately after the residual gasoline. The pretreating liquid, e.g.acetone, containing the desorbed nitrogen compound then follows. As aresult, the acetone need not come into contact with the elutriatedhydrocarbon oil. The hydrocarbon oil and water may, of course, beseparated simply by settling into two phases. Thus removal of nitrogencompounds from hydrocarbons, including the residual gasoline which ispresent in the adsorption zone at the time of the regeneration cycle maybe effected without the necessity of distilling the treated product. Theregeneration may be effected merely by contacting the adsorbent with thepolar liquid alone. After treatment of the adsorbent with polar organicliquid, following the desorbing operation in which water was also used,the adsorbent is again ready for use. The nitrogen compounds may berecovered from the polar organic liquid by fractionation of theelutriated mixture.

The invention may be more readily understood from the followingillustrative examples:

Example I Silica gel was wetted with acetone. In order to prevent anundesirable rise in temperature and if possible to fill all pores withacetone the silica gel was immersed in acetone. Twenty grams of thesilica gel thus wetted were introduced into a vertical glass tube havingan inside diameter of 17 mm. There was introduced into the top of thetube a gasoline obtained by catalytic cracking of a mineral oil andhaving a boiling range of from 40 C. to 205 C. The gasoline waspreviously made doctor-sweet by a treatment with a dilute aqueouscaustic solution followed by an air solutizer sweetening treatment asdescribed in British patent specification No. 775,015, the treatedgasoline having a content of nitrogen compounds of 6.5 milli-equivalentsper litre, viz. 0.0116% by weight (calculated as nitrogen). The gasolinewas passed through the tube at the rate of 450 cc. per hour. Thegasoline issuing from the tube was substantially free from nitrogen.After approximately 2500 cc. of gasoline had been passed through thetube the silica gel was found to be saturated with nitrogen compounds,from appearance of nitrogen compounds in the effluent gasoline.

The silica gel was then regenerated. In order to expel the gasolinepresent in the tube, 50 cc. of a 1:1 by volume mixture of acetone andwater were first passed through the tube. Following the gasoline, waterissued from the tube. These liquids could be readily separated.Nitrogen-containing acetone, containing 0.8 milliequivalent of nitrogenper gram of silica gel then flowed from the tube. Hence 11.2 mg. ofnitrogen had been bound and subsequently eluted, per gram of silica gel.After the treatment with the mixture of acetone and water, 50 cc. ofacetone were passed through the tube, as a result of which the silicagel was again ready for use.

After five cycles of nitrogen removal and regeneration, the capacity ofthe silica gel was found to have been only slightly reduced. Originallythis capacity Was 0.8 milliequivalent of nitrogen per gram of silicagel. After regenerating five times, 0.5 milli-equivalent of nitrogencould be adsorbed per gram of silica gel. After regenerating 15 times,the capacity was still 0.5 milli-equivalent of adsorbed nitrogen pergram of silica gel.

Example 11 Twenty grams of silica gel having a particle size of 0.2-1mm. diameter were introduced into a vertical tube having an insidediameter of 17 mm. The height of the silica gel bed was 12 cm. Thesilica gel had been previously immersed in ethyl acetate.

A gasoline obtained by catalytic cracking, boiling be tween 40 C. and205 C. and pretreated in the same manner as described in Example I, waspassed into the top of the tube at the rate of 450 cc. per hour. Thisgasoline had a nitrogen content of 0.0116% by weight. The gasolineflowing from the tube was substantially free from nitrogen.

After 3,000 cc. of gasoline had been passed through, the bed was foundto be saturated with nitrogen compounds.

The silica gel bed was again prepared for further use by passing cc. ofethyl acetate through the bed. The gasoline and the nitrogen compoundsadsorbed on the silica gel were washed out by the ethyl acetate. Fromthe collected mixture of nitrogen compounds, gasoline and ethyl acetateit was possible to separate the ethyl acetate from the nitrogencompounds by distillation.

Example III Twenty-five grams of silica-alumina gel having a particlesize of approximately 0.2 mm. were introduced into a vertical tubehaving an inside diameter of 17 mm. This silica-alumina had been used asa catlyst in a cracking plant for the production of cracked gasoline.The height of the bed formed was 12 cm. The catalyst had been previouslyimmersed in acetone.

A gasoline obtained by catalytic cracking and boiling between 40 C. and205 C. was passed into the top of the tube at the rate of 450 cc. perhour. This gasoline had a nitrogen content of 0.0116% by weight. Afterthe treatment the gasoline was substantially free from nitrogen.

After 1,000 cc. of gasoline had been passed through the bed was found tobe saturated with nitrogen compounds.

The bed was again prepared for further use by passing 90 cc. of acetonethrough it. The gasoline and the nitrogen compounds adsorbed on thesilica-alumina was washed out. From the collected mixture of nitrogencompounds, gasoline and acetone it was possible to separate the acetonefrom the nitrogen compounds by distilation.

Example IV Twenty grams of silica gel having a particle size of 0.21 mm.diameter, previously immersed in acetone, are introduced into a verticaltube having an inside diameter of 17 mm., to a bed height of 12 cm.

A light gas oil obtained by catalytic cracking, having a gravity of34.8" API, and boiling between 198 C. and 343 C. is passed into the topof the tube at the rate of 325 cc. per hour. This gas oil has a nitrogencontent of 0.015% by weight. The gas oil flowing from the tube issubstantially free from nitrogen until after 2,100 cc. of light gas oilare passed through the bed.

The silica gel is again prepared for further use by passing through thetube 50 cc. of a mixture of acetone and water in the ratio by volume of1: 1. The gas oil issues from the tube followed by the water and the twoare readily separated by settling. The nitrogen-containing acetone thenflows from the tube, from which mixture the acetone is removed bydistillation. Approximately 20 cc. of acetone are then passed throughthe column to pre-wet the adsorbent for another adsorption cycle.

Example V Twenty grams of silica gel having a particle size diameter of0.2-1 mm. and pre-wet by immersion in diethyl ether are introduced intoa vertical column, having an inside diameter of 17 mm., to a gel bedheight of 12 cm.

A gasoline obtained by catalytic cracking and boiling between 40 C. and205 C. is passed into the top of the tube at the rate of 450 cc. perhour. This gasoline had a nitrogen content of 0.0116% by weight. Thegasoline flowing from the column is substantially free of nitrogen untilover 2,500 cc. of gasoline have been passed through the bed.

The silica gel is prepared for further use by passing 75 cc. of diethylether through the bed. The gasoline and nitrogen compounds are desorbedfrom the silica gel and washed out by the diethyl ether. From thecollected mixture of nitrogen compounds, gasoline and diethyl ether, itis possible to separate the diethyl ether from the nitrogen compounds bydistillation.

Example VI A column 12 cm. in height is prepared from 20 grams of silicagel having a particle size diameter of 0.2-1 mm. and previously immersedin ethanol.

A catalytically cracked gasoline boiling between 40 C. and 205 C. andhaving a nitrogen content of 0.0116% by weight is passed through thecolumn at the rate of 400 cc. per hour. The gasoline flowing from thecolumn is substantially free of nitrogen. After 2,300 cc. of gasolinehas been passed through, the bed is found to be saturated with nitrogencompounds.

By passing 85 cc. of ethanol through the bed, the gasoline and nitrogencompounds removed from the gasoline are desorbed and washed from thecolumn. No further washing with ethanol is necessary and the column isregenerated and ready for further use.

Example VII Twenty grams of silica gel having a particle size diameterof 0.2-1 mm. and pre-wet by immersion in dioxane are introduced into avertical tube, having an inside diameter of 17 mm., to a bed height of12 cm.

A gasoline obtained by catalytic cracking and boiling between 40 C. and205 C. is passed into the top of the tube at the rate of 400 cc. perhour. The effiuent gaso line, which had a nitrogen content of 0.0116% byweight prior to treatment by this process, is substantially free fromnitrogen until after 3,000 cc. of gasoline have been passed through thebed.

The silica gel bed was prepared for further use by passing 90 cc. ofdioxane through the bed of adsorbent. The gasoline and nitrogencompounds are thusly desorbed from the silica gel and washed out by thedioxane. The components of the elutriant wash liquid solution are thenseparated by distillation.

Since this invention is carried out in the liquid phase, the operatingpressure has no substantial effect on the adsorption characteristics ofthe process. Therefore, the choice of operating pressures will begoverned largely by pressure drop and throughput requirements.

It is, of course, known that temperature generally reduces theadsorptivity of a compound. However temperature also reduces theadsorptivity of the polar organic liquid to about the same extent.Therefore, since the relative adsorptivities of the components to beseparated and the polar organic liquid determine the selectivity; andfurther, since their relative adsorptivities re-' main about the same,it may readily be seen that there is no marked shift in selectivity tobe obtainned by varying the temperature of the process. Of course,extreme variations can significantly affect the relative adsorptivityand therefore it is preferred to carry out the process between about 20C. and 60 C. However, successful operation is not limited to this rangeexcept as the relative adsorptivity of the polar organic liquid andnitrogen compounds to be removed may be changed thereby to the extentthat the desired degree of selectivity is destroyed. The comparativelylow temperatures at which this process may be carried out is, of course,advantageous in that it reduces further the risk of chemical conversionof the oil components when in contact with the adsorbent.

It will be recognized by those skilled in the art that the efiiuen'tfrom the column must, during the nitrogen removal step, be equilibratedwith the column. That is, the fluid being treated must be ofsufficiently low viscosity that all of the nitrogen compounds havesufiicient residence time within the column to be diffused through theliquid hydrocarbon solute phase to the adsorbing surface. It is thusanother effect of higher temperature, due to lower viscosity, thatbetter establishment of equilibrium can take place. Oils having too highviscosity to allow proper diffusion of the nitrogen compounds maynevertheless be treated by this process by diluting them with a lowviscosity solvent having a very low adsorptive affinity such as lowmolecular weight liquid paraflinic hydrocarbons, e.g., pentane. Fromthis, it will also be understood that the space velocity of oil throughthe column must be sufficiently low to equilibrate the efliuent to thecolumn of adsorbent in order to avoid incomplete removal of nitrogencompounds. It is generally preferred not to exceed-a liquid hourly spacevelocity of 60 volumes of oil per volume of adsorbent per hour. Theshort residence times, which characterize this process for the removalof nitrogen compounds, are additionally advantageous in that thelikelihood of chemical conversion of the oil components when in contactwith the adsorbent is even further reduced.

It is a further advantage of the process of this invention that theamount of polar organic liquid (washing liquid) required to desorb theremoved nitrogen compounds is small, thus significantly decreasing theinitial capital expense and solvent costs for the commercial practice ofthe invention. It is of interest to note that the amount of washingliquid required is substantially unaffected by the ratio of adsorbent totreated oil, and is primarily a function of the amount of adsorbent. Itis preferred to use a minimum of about 1 ml. of washing liquid per gramof adsorbent, still better at least 2 ml. Greater degrees of ertectiveness of desorption may be obtained at even higher ratios,however, such ratios in excess of about 3 ml. per gram unduly increasethe cost of solvent, solvent recovery, and equipment. v

t is a very attractive feature of the process of the invention that theregeneration of the adsorption is very rapid as well as complete. Theregeneration period is much shorter than the adsorption period and henceis not a limiting factor in the practice of the process of a cyclicprocess. Thus, the process may be carried out on a continuous feed basiswith only two adsorber columns in parallel one of which is regeneratedwhile the other is adsorbing. However, because of the rapidity withwhich the regeneration is completed, it is not necessary to resort tointermittent operation of the adsorbers. The process may be carried outcontinuously, for example in a vessel having fixed inlet and outletnozzles above and below a rotating bed of adsorbent. Conversely, avessel having a fixed bed of adsorbent with rotating inlet and outletnozzles can also be used. It is, of course, to be understood that thepractice of the invention is not limited to fixed bed operation whereinthe liquid is passed through the adsorbent, but may be adapted to othermodes of operation, such as placing the adsorbent in the liquid to betreated and then separating the adsorbent from the treated liquid byfiltration or other liquid-solids separation means.

We claim as our invention:

1. A process for the removal of dissolved organic nitrogen compoundsfrom liquid hydrocarbons by contacting the liquid hydrocarbon with theentire body of a solid adsorbent having adsorptive surfaces pre-wet witha polar organic liquid having an adsorptive afiinity for the solidadsorbent approximately equal to the adsorptive afiinity for theadsorbent of the dissolved organic nitrogen compounds to be removed andin which said polar organic liquid is an organic compound containingoxygen, selected from the group consisting of dialkyl ketones, alkylesters, dialkyl ethers, cyclic ethers, alkanols, alkanediols, andalkanediol monoethers, separating the hydrocarbons from the adsorbentand adsorbate comprising at least a portion of the nitrogen compounds,desorbing the adsorbate nitrogen compounds from the adsorbent, andregenerating and pre-wetting the adsorbent for further use with at leastone milliliter of said polar organic liquid per gram of adsorbent.

2. The process of claim 1 in which the adsorbent is a high surface areainorganic compound containing oxides of metals selected from the groupconsisting of silicon and aluminum.

3. The process of claim 2 in which the adsorptive agent is silica gel.

4. The process of claim 2 in which the adsorptive agent is alumina.

5. The process of claim 1 in which the polar organic liquid is a dialkylketone having less than six carbon atoms per molecule.

6. The process of claim 5 in which the polar organic liquid is acetone.

7. The process of claim 1 in which the polar organic liquid is a fattyacid alkyl ester having no more than six carbon atoms per molecule.

8. The process of claim 7 in which the polar organic liquid is ethylacetate.

9. The process of claim 1 in which the polar organic liquid is a dialkylether, having no more than six carbon atoms per molecule.

, 10. The process of claim 9 in which the polar organic liquid isdiethyl ether.

11. The process of claim 9 in which the polar organic liquid isdiisopropyl ether.

12. The process of claim 1 in which the polar organic liquid is a cyclicether having no more than six carbon atoms per molecule.

13. The process of claim 12 in which the polar organic liquid isdioxane.

14. The process of claim 1 in which the polar organic liquid is analkanol having no more than six carbon atoms per molecule.

15. The process of claim 1 in which the polar organic liquid is analkanediol having no more than six carbon atoms per molecule.

16. The process of claim 1 in which the polar organic liquid isalkanediol monoether having no more than six carbon atoms per molecule.

17. A process for the removal of dissolved organic nitrogen compoundsfrom liquid hydrocarbons by contacting said liquid hydrocarbon with theentire body of a solid adsorptive agent, the adsorptive surfaces ofwhich have been pre-wetted with acetone, wherein the removed nitrogencompounds are desorbed from the adsorptive agent, and said adsorptiveagent is regenerated and prewetted for further use by first contactingsaid adsorbent with at least one milliliter of a mixture consisting ofequal parts by volume of acetone and water per gram of adsorbent, andsubsequently contacting said adsorbent with acetone.

18. The process of claim 17 in which the liquid which is to be treatedis a nitrogen-containing hydrocarbon obtained by the thermal orcatalytic cracking of higher boiling mineral oils.

19. The process of claim 18 in which the liquid hydrocarbon to betreated is a cracked gasoline.

20. A process for the removal of dissolved organic nitrogen compoundsfrom liquid petroleum hydrocarbons by passing said liquid hydrocarbonsin contact with and through the entire body of a solid adsorptive bodyin a column, the surfaces of said body being pre-wet with a polarorganic liquid having an adsorptive aflinity for the body approximatelyequal to that of the nitrogen compounds and in which said polar organicliquid is an organic compound containing oxygen, selected from the groupconsisting of dialkyl ketones, alkyl esters, dialkyl ethers, cyclicethers, alkanols, alkane diols, and alkanediol monoethers, separatelyremoving the bulk of the sotreated hydrocarbons from the column,desorbing the adsorbate nitrogen compounds from the solid with adesorbent consisting essentially of the pre-wetting polar com pound,whereby the adsorbent is regenerated and prewetted for further use withat least 1 milliliter of the polar organic liquid per gram of adsorbent.

21. A process according to claim 20 wherein, following removal of themain bulk of the liquid hydrocarbons, pre-wetting polar liquid mixedwith water is introduced into the column, polar liquid remaining on theadsorbent and water advancing through the adsorbent and passing out ofthe column, whereby remaining liquid hydrocarbons are swept out of thecolumn, and thereafter introducing substantially anhydrous pre-wettingpolar liquid, the total amount of said liquid on the adsorbent thenbeing at least about 1 milliliter per gram of adsorbent.

References Cited in the file of this patent UNITED STATES PATENTS2,728,715 Rampino Dec. 27, 1955 2,763,603 Skinner Sept. 18, 19562,779,718 Capell et al Jan. 29, 1957 2,925,379 Fleck et .al Feb. 16,1960 2,925,380 Fleck et al Feb. 16, 1960

1. A PROCESS FOR THE REMOVAL OF DISSOLVED ORGANIC NITROGEN COMPOUNDSFROM LIQUID HYDROCARBONS BY CONTACTING THE LIQUID HYDROCARBON WITH THEENTIRE BODY OF A SOLID ADSORBENT HAVING ADSORPTIVE SUSRFACES PRE-WETWITH A POLAR ORGANIC LIQUID HAVING AN ADSORPTIVE AFFINITY FOR THE SOLIDADSORBER APPROXIMATELY EQUAL TO THE ADSORPTIVE AFFINITY FOR THEADSORBENT OF THE DISSOLVED ORGANIC NITROGEN COMPOUND TO BE REMOVED ANDIN WHICH SAID POLAR ORGANIC LIQUID IS AN ORGANIC COMPOUND CONTAININGOXYGEN, SELECTED FROM THE GROUP CONSISTING OF DIALKYL KETONES, ALKYLESTERS, DIALKYL ETHERS, CYCLIC ETHERS, ALKANOLS, ALKANEDIOLS, ANDALKANEDOIL NONOETHERS, SEPARATING THE HYDROCARBONS FROM THE ADSORBENTAND ADSORBATE COMPRISING AT LEAST A PORTION OF THE NITROGEN COMPOUNDS,DESORBING THE ADSORBATE NITROGEN COMPOUNDS FROM THE ADSORBENT, ANDREGENERATING AND PRE-WETTING THE ADSORBENT FOR FURTHER USE WITH AT LEASTONE MILLILITER OF SAID POLAR ORGANIC LIQUID PER GRAM OF ADSORBENT.